Holiday calendar: Circle of power

A picture taken by the GeoEye 1 satellte on Nov. 4, 2010, shows the Gemasolar power-generating array in Seville, Spain. At the center of the array is a 40-story-high concrete tower, ringed by 2,650 mirrors. The mirrors focus sunlight on the tower, which stores the heat and converts it to energy.

Like Stonehenge, the array is laid out geometrically to track the position of the sun. But Gemasolar isn't meant to mark the year's astronomical milestones. Instead, it will concentrate sunlight to provide power for 25,000 homes around the city of Seville.

The light is focused by 2,650 large mirrors on a 450-foot-high concrete tower, with a central core that heats up to 1,650 degrees Fahrenheit (900 degrees Celsius). The energy is transferred to molten salt for storage, and the heat of the salt drives steam turbines that generate electricity even when the sun isn't shining. The $325 million plant had its official inauguration in October and is due to reach full operation in 2013. At its peak, the concentrated solar-power plant should be able to produce 19.9 megawatts of power.